Design and performance of the LHCb Silicon Tracker

1. Design and performance of the LHCb Silicon Tracker Introduction Silicon Tracker project: design production Tracking strategy and performance Kim Vervink Ecole Polytechnique Fédérale de Lausanne TIME 05 - Zurich

2. 250 mrad 10 mrad p p A huge one arm spectrometer. Dipole Magnet Tracking Systems Vertex Locator Muon Chambers Calorimeters Rich 1 & 2 Precision measurements of CP violation and rare decays in the B sector Kim Vervink

3. Neighbouring detectors of the Silicon Tracker. The vertex locator R – f detector strip orientation 21 stations around the interaction point 1m The other subdetector that uses silicon Half discs open during beam injection and close around the interaction point up until 8 mm Whole subdetector in vacuum Silicon thickness: 300 mm Kim Vervink

4. the outer tracker Outer Tracker 3 stations with 4 double planes 4,7 m! OT Straw tubes 5mm diameter Pitch 5,25 mm Module production going to completion Kim Vervink

5. Silicon Tracker Project Some participants Involved institutes: M.I.P. – Heidelberg E.P.F.L. – Lausanne U.S.C. – Santiago de Compostela UniZh – Zurich Kim Vervink

6. Challenges of the Silicon Tracker. • Large areas have to be covered in Silicon. The Silicon design is adapted in order: • to keep it affordable • not to become overloaded in readout channels  Long readout strips • Large distance between readout strips • 2. Bunch crossings every 25ns •  fast shaping time • 3. Momentum resolution is limited by multiple scattering •  minimization of material for the acceptance: Thin sensors • More load capacitance which increases the noise • Beetle chip front-end design • Adapted sensor thickness • Decreases S/N between strips •  optimise width/pitch of the strips Increases noise  Optimised front-end electronics Thinner sensors make S/N go down  Best compromise Kim Vervink

7. TT VELO Where is the Trigger Tracker? Located behind the Velo & Rich 1 Just in front of the Magnet: still in frindge field Active area of the detector covers full acceptance (cooling and electronics outside) 2 half stations in one box with in total 4 detector planes (0°, 5°, -5°, 0° orientation) Kim Vervink

8. Trigger Tracker Staggered front-end readout hybrids Silicon sensors Pitch adaptor Interconnect cable Kim Vervink Support rails

9. Where is the Inner Tracker? Inner Tracker consists out of 3 stations, surrounded by the Outer Tracker 2 boxes with 2 Si-sensors modules 2 boxes with 1 Si-sensor modules TT VELO Complete IT detector inside the acceptance (hybrids,pcb’s, cooling, cabling, …) Kim Vervink 1,3 % of acceptance, 20% of tracks.

10. Si-sensor Pitch Adaptor + hybrid with Beetles. Kapton insulation Aluminium Mini-Balcony • Ladders are attached via the mini-balcony on a cooling rod, through which runs a cooling liquid • detector is cooled (10°C) • in order to control the thermal runaway Airex foam Carbon Fiber support layer: helps the cooling flow to the sensors Readout Cables, High and Low voltage cables Cooling System Kim Vervink

11. Silicon sensors for a fast and precise measurement. Bond pads & DC readout! HV input to the backside of the sensor Left strip Right strip S/N value is above 12, taking into account the charge loss between strips. Kim Vervink

12. Production Status Trigger Tracker: 2 half stations with 280 (+15% spare) readout sectors have to be build Inner Tracker: 3 stations with 336 (+15% spare) modules are to be produced and tested A typical production trategy: Building of a module using jigs (parallel production) Metrology Electrical test using internal test pulses in order to find broken or unbonded strips Schedual: Prototyping finished in August for both detectors Start of production All modules need to be fabricated by April 2006 Installation in the LHCb pit in June 2006 Status: Inner Tracker has about 20 modules produced Trigger Tracker has 13 modules fabricated Inner tracker testing box Kim Vervink

13. A Trigger Tracker module and burn-in test setup A built TT module Cooling system Kapton readout cable 4 modules Burn-in box Sensor TT burn-in test Hybrid Kim Vervink

14. Support and IT modules are in theproduction phase… The 2nd short ladder module that was made… Setup of the support frame Kim Vervink

15. Silicon project: essential part for the tracking of the LHCb detector • Reconstruction is not a trivial task • LHCb gets about 50 primary particles per event: check…. • 30% radiation length between interaction point and Rich2 • Secondary particles • Multiple scattering • Degrades the momentum resolution Interaction every 25 ns • Spillover from previous bunch crossings Kim Vervink

16. Tracking reconstruction Particles spread out by magnet. Bdl = 4 Tesla m Warm magnet Top view • Multipass strategy • Long tracks • Ks after Velo • Only Velo and TT Kim Vervink

17. First look for tracks that pass the whole tracking device (from Velo to T) Easiest to find Highest track resolution The most important ones for physics studies  Start with a Velo Seed ( almost straight line: only position and direction known) Adding one T station measurement to a Velo track Use optical parameterisation to calculate where the track passed using zCenter and dSlope Use the other measurements of the T stations to confirm hypothesis Fast algoritm: main tracking done in HLT Tracking strategy Optical method parametrisation zCenter dSlope Kim Vervink

18. Second pass of long track reconstruction: • work backwards • Seeding: • Seeding in T stations using unused hits Three hits define an ”almost” straight line Collect more hits around “trial track” to confirm your hypothesis Also used to optimise Rich2 performance Tracking: Transport the track seed to the Velo and compare with a Velo seed  Look at the difference of track parameters • Use c² criteria for matches This method adds about 3% to the overall long track finding efficiency Kim Vervink

19. Other track types • Of the remaining hits, make tracks from particles that passed only in TT and IT/OT • Most are decay products of a Ks that decay outside VeLo • Look for unused seeds in the T stations and add hits in TT • Use optical method again. • Look amongst the remaining particles for hits in the Velo and TT stations alone. • Particles with low momentum: bent out by magnetic field • Look for unused Velo tracks with hits in the TT detector • Moderate efficiency (70%) and resolution (dp/p ~ 15%) but used to improve RICH 1 performance, kaon tagging and to find slow p from D* Kim Vervink

20. Tracking Performance on long tracks Cut out in physics analysis Momentum dependent: B particles have higher momentum Track finding efficiency ~95% Kim Vervink

21. Performance on the resolution of the momentum and the impact parameter (long tracks) Kim Vervink

22. The design and prototyping of the Silicon Tracker subdetectors is finished. Production of both the Silicon Tracker has started and Installation in the LHCb pit is schedualed in June 2006. Tracking performances are highly dependent on the quality of the Silicon Tracker detector. A tracking strategy has been implemented, and its performance is satisfactory. Summary Kim Vervink